Method and apparatus for applying particulate coating material to a work piece

ABSTRACT

A system for applying particulate coating material to a work piece in which the particulate material is directed against the work piece in a series of pulses. Each pulse includes an initial step of feeding a charge of combustible gaseous mixture into a combustion chamber provided with an outlet nozzle. The combustible mixture is ignited and the outflow of gaseous mixture through the nozzle is constricted sufficiently to cause a rapid pressure rise during combustion to a peak value, followed by a period of falling pressure during continued outflow of the combusted mixture through the nozzle. A charge of the particulate coating material is injected into the combustion chamber for a brief period which terminates while the pressure in the chamber is at least a substantial proportion of the peak pressure. The outflow of combustion mixture and entrained particulate material is directed through the nozzle at high velocity against the work piece to cause the particulate material to form a coating on the work piece.

'United States Patent [191 Melton, Jr. et al.

[4 1 Oct. 28, 1975 [54] METHOD AND APPARATUS FOR APPLYING PARTICULATECOATING MATERIAL TO A WORK PIECE [75] Inventors: Rosser Melton, Jr.,Helotes; John M. Clark, Jr., Seguin; Ronald J. Mathis, San Antonio;William D. Weatherford, Jr., San Antonio; Charles D. Wood, III, SanAntonio, all of Tex.

[73] Assignee: Southwest Research Institute, San

Antonio, Tex.

[22] Filed: Oct. 26, 1973 [21] Appl. No.: 409,962

Related US. Application Data [62] Division of Ser. No. 198,806, Nov. 15,1971, Pat. No.

[52] US. Cl. 239/81; 239/85; 239/101; 117/22; 117/105 [51] Int. Cl.B0515 l/24; C23C 7/00 [58] Field of Search 239/79-81, 239/85, 70, 99,101; 117/22, 105, 105.1, 105.2, 46 ES [56] References Cited UNITEDSTATES PATENTS 2,714,563 8/1955 Poorman et al. 117/22 X 2,774,62512/1956 l-lawley et al. 239/81 X 2,861,900 ll/1958 Smith et al 117/1052,950,867 8/1960 Hawley et al. 239/79 X Primary ExaminerR0bert S. Ward,Jr. Attorney, Agent, or F irml-1ubbard, Thurman, Turner & Tucker [57]ABSTRACT A system for applying particulate coating material to a workpiece in which the particulate material is directed against the workpiece in a series of pulses. Each pulse includes an initial step offeeding a charge of combustible gaseous mixture into a combustionchamber provided with an outlet nozzle. The combustible mixture isignited and the outflow of gaseous mixture through the nozzle isconstricted sufficiently to cause a rapid pressure rise duringcombustion to a peak value, followed by a period of falling pressureduring continued outflow of the combusted mixture through the nozzle. Acharge of the particulate coating material is injected into thecombustion chamber for a brief period which terminates while thepressure in the chamber is at least a substantial proportion of the peakpressure. The outflow of combustion mixture and entrained particulatematerial is directed through the nozzle at high velocity against thework piece to cause the particulate material to form a coating on thework piece.

7 Claims, 10 Drawing Figures US. Patent Oct. 28,1975 Sheet1of4 3,915,381

Ava 60 966 Fssem/o/ U.S. Patent Oct. 28, 1975 Sheet 2 of4 3,915,381

ISQQQQQ ls fins, M144 lascm'os Cow/1Y6 P679100 US. Patent Oct. 28, 1975Sheet 3 of4 3,915,381

METHOD AND APPARATUS FOR APPLYING PARTICULATE COATING MATERIAL TO A WORKPIECE RELATED APPLICATION This is a divisional application of copendingapplica tion Ser. No. l98,806,"fild Nov. 15, l97l, now US Pat. No.3,801,346. This invention relates to a" method and apparatus forapplyingiparticulate coating'ma'terial to a work piece, and inparticular to a system in which the coating material is directed intermit tentl y' against the work piece in a heated condition in ahighvelocity gas stream.

applying coating materials, it is advantageous with certain materials inview of their high melting points, non-galvanic properties or forotherreasons, to direct the coating material in particulate form against awork piece in a high velocity gas stream'at an elevated temperature. Ifthe conditions are carefully chosen, the particles of coating materialbecome fl attened and weld melting during continuous operation mayrender the apparatus unduly heavy and cumbersome.

It may sometimes be desirable, therefore, to utilize an intermittant orpulsed coating system. ln one such prior system, a combustible gaseousmixture is ignited in a combustion chamber at the upstream end of a gunbarrel which is sufficiently long to permit a supersonic detonation waveto be established in and travel down the barrel. Downstream of thecombustion chamber particulate coating material is fed into the gunbarrel so that the particles are carried down the barrel at highvelocity and directed against a suitable work piece. Again, althoughgenerally satisfactory for its intended use, a prior device of thissecond type may also be unsatisfactory under certain conditions. Forexample, the need to have a sufficiently long barrel on the device tosustain a supersonic detonation wave may make the device unnecessarilylengthy for installation at locations where space is at a premium.Additionally; by injecting the to each otherandto the workpiece toproducea hard,

non-porous coating. 7

[n.performinga coating process of this general nature, it has, beenfoundthat at least three variables are of critical importance, the rate atwhich material is deposited,.the velocity at which the particles hit thesurface and, the temperature at impact of the particles which is afunction both of the temperature to which they areraised in the gasstream and their kinetic energy on impact which is converted into anadditional temperature rise. Various prior coating systems havetherefore been devised intended to providea suitable degree of' controlover these coating process variables.

For-example, oneprior-"coating system utilizes a tubular housing fedwith continuous streams of acetylene, oxygemand a carrying gas (whichmay also be oxygen) containing powdered coating material. The gases areignited continuously within the tubular housing and directed down awater-cooled barrel to impinge upon the work piece in acontinuous-stream at-a velocity of at least 2,000 feet per second.Although such a system may be'generally satisfactory for the purpose forwhich itis intended, certain problems may arise underparticularcondit-ions. For example, a continuously operating systemsubjects the workpiece to a large uninterrupted stream of very hot burntgases which could easily overpowder at a location downstream of thecombustion zone, the opportunity to heat the powder directly in thecombustion zone is los'tJAlso, by the time the detonation wave reachesthe powder injection zone downstream of the combustion zone, some of thepeak pres-' zone has necessarily sure-attained in the combustion alreadybeen dissipated.

SUMMARY OF THE INVENTION The present invention provides a method andappara- .tus for applying particulate coating material to awork eouscombustible mixture into a combustion chamber heat the work.-piece-an"dsubject it to severe thermal erosion or distortioiizfln addition, such asystem operatin'gcontinuously at velocities in'the order of 2,000 feetper second would'tend to deposit-coating material at a very high rateand on certain types of small work pieces this rate of coating build-upmight 'not allow heat to escape from the work piece sufficient rapidly,thereby further contributing to'thermal distortion of the work piece.Another problem with 'such'a system may be inefficient utilization offuel as a continuous gas flow system usuallyrequires that the proportionof powder in the combustion gases be about 5-10% ofgas mass as highconcentrations would supply material so rapidly as to "even furthercompoundthe heat dissipation problems just described To avoid thesepotential hazards, it wo uld be preferable to emply a pulsedsystemallowing tiine between applications of coating material in whichsufficient heat dissipation from the work piece could occur to avoiddistortion; Additionally, the need fora water cooled barrel to preventthe barrel from provided with an outlet nozzle. The combustible mixtureis ignited and the outflow of gaseous mixture through the nozzle isconstricted sufficiently to cause a rapid pressure rise duringcombustion of the mixture tively, approximately at the time the pressurein the combustion chamber reaches its peak value andterminating whilethe pressure in the chamber is still a substantial proportion of thepeak pressure. The outflow of combusted mixture and entrainedparticulate material is directed through the nozzle against the workpiece at high velocity to cause the particulate material to for acoating on the work piece. I

It will be appreciated that by using a pulsed system, the rate ofapplication of material to the work piece is reduced sufficiently topermit the work piece to dissipate some of the heat between successiveapplications of coating material thereby minimizing the possibility ofdistortion. Pulse operation also provides more effecient use of fuel asthe wastage of combusted gases occurring during a continuous flowagainst the work piece is avoided. By terminating the entry ofparticulate material into the chamber while the pressure is still a sub?stantial proportion of the peak pressure, it is insured that almost allthe particulate material is applied to the work piece while the velocityof the outgoing stream is still sufficiently high to form a satisfactorycoating.

Thus. by the time the velocity of the stream has mately 400 psi, and avelocity of outflow of the com-.

busted gases of about 3,000 feet per second with the entrainedparticulate material traveling at about L500 feet per second.

BRIEF DESCRIPTION OF THE DRAWINGS An apparatus for applying particulatecoating material to a work piece, constructed in accordance with onepreferred embodiment of the invention, is illustrated in theaccompanying drawings in which:

FIG. I is a side view of an apparatus for applying particulate coatingmaterial, constructed in accordance with the preferred embodiment of theinvention, showing certain principal elements of the apparatus includinga combustion chamber, a fuel inlet unit, and a powder injector, r

FIG. 2 is a schematic view of a source of combustible gaseous mixturefor supplying the apparatus shown in FIG. 1,

FIG. 3 is a cross-sectional side view of the combustion chamber shown inFIG. 1,

FIG. 4 is a schematic circuit diagram of an ignition circuit for a sparkplug connected with the combustion chamber shown in FIG. I,

FIG. 5 is a timing diagram showing the relative periods of operation ofvarious of the principal elements shownin FIG. 1,

FIG. 6 is a cross-sectional side view of the fuel inlet unit shown' inFIG. 1, v I

FIG. 7 is a cross-sectional top view of thefuel inlet unit shown in FIG.6 taken along the lines 77 therein,

FIG. 8 is a cross-sectional side view of the powder injector shown inFIG. 1,

FIG. 9A is a schematic electrical circuit diagram showing the electricalconnections to an electrical solenoid forming a part of the fuel inletunit shown in FIG. 6; and

FIG. 9B isa schematic graph of current and voltage versus time for theelectrical circuit shown in FIG. 9A.

Referring now to the drawings, and particularly to FIG. lot thedrawings, an apparatus for applying particulate coating material,constructed in accordance with the preferred embodiment of theinvention, is

shown.

The components of the unit include a combustion chamber 2 shapedgenerally like an inverted bulb and a downwardly directed nozzle 4through which particulate coating material entrained in a high velocitygas stream is directed in intermittent pulses at an underlying workpiece 6. Associated with the combustion chamber 2 are, a fuel inlet unit8 for periodically feeding a charge of combustible gaseous mixture intothe combustion chamber 2, a spark plug 10 mounted on the combustionchamber projecting into its interior to ignite the charge of combustiblemixture and a powder injector unit 12 for feeding in a charge of theparticulatematerial. Many particulate materials may be used includinghigher melting point coating materials such as tungsten carbide, as wellas flaked metal coatings and other coatings. A separate description ofthese components follows.

The combustion chamber 2, which is formed of steel or similar material,is configured generally as an inverted bulb witha flattened, enlargedupper end region of mean diameter D (FIG. 3) tapering down to a reducedneck portion. Welded to the free lower extremity of the neck of thecombustion chamber 2 is a block 20 which is threaded to receive thecorrespondingly threaded upper end of the previously mentioned nozzle 4which is a short pipe aligned concentrically with the vertical axis ofthe'combustion chamber 2.

A horizontal bushing 22 extends through the wall of the combustionchamber 2 into its interior in the upper, enlarged region of thecombustion chamber. The bushing 22 is threaded internally and mountscorrespondingly threaded portions of the previously mentioned fuel inletunit'8. Periodically (as will be described hereinafter) the fuel inletunit 8 injects a charge of combustible gaseous mixture, which in thepreferred embodiment is a mixture of propane gas and air, into theinterior of the combustion chamber 2.

The mixture is then ignited by the previously mentioned spark plug 10(FIG. 1) which is tapped through the wall of the combustion chamber 2projecting into its interior. The spark plug is positioned centrally ofthe enlarged upper portion of the combustion chamber displaced from theinlet unit 8. Other locations may be chosen for the spark plug. Thespark ignition plug 10 is a conventtional automobile spark plug which,when it is energized, initiates a flame front that extends through thecharge of combustible mixture.

' In an important aspect of the invention, combustion within the chamberis by deflagration as opposed to detonation, by which it will .beunderstood that the flame front proceeds through the mixture in thecombustion chamber at a subsonic velocity, which is about 75 feet persecond. In the preferred embodiment it is contemplated that thecombustion of the mixture occurs entirely by deflagration.

In an alternative embodiment of the process, however, the chamber 2 maybe so dimensioned that the ,last part of combustion is by auto-ignitionin which spontaneous ignition of the end gas at substantially all thepoints in it occurs simultaneously.

An important characteristic of the chamber in attaining a sufficientpressure rise during combustion to provide a satisfactory coating is theratio between the diameter of the upper, enlarged portion of thecombustion chamber 2 and the diameter of the outlet nozzle 4. In thepreferred example the combustible propane air mixture is admitted to thechamber 2 at about psi and it is necessary to achieve a pressure rise toa peak value during combustion of about 400 psi. If the outlet nozzle 4has too large an internal diameter, too much gaseous mixture may escapethrough the nozzle before the pressure has built up sufficiently. Toachieve such a pressure it has been found that the ratio of the meaninternal diameter D of the combustion chamber of the enlarged upperregionto the internal diameter of the nozzle 4 (d in FIG. 3) should beat least 5 to I and preferably somewhat greater. For example in thepreferred embodiment where the internal diameter d of the nozzle 4 isone-third inch, the chamber diameter D in its enlarged-region is about2% inches providing a ratio of D/d of 7 /2. Stated in another way, theratio V/d should exceed about 50 where V is the volume of the chamber incubic inches and d is the diameter of the opening. Of course if a lengthof the chamber becomes significantly greater than the diameter of thechamber, the time required for the flame to propagate throughv thechamber may become so great as to materially reduce the pressuresreached in the chamber because of the escape of gas through the opennozzle during the period of deflagration. The combustion chamberpressures and dimensions described result in a gas velocity through thenozzle of about 3,000 feet per second with the velocity of the entrainedpowder being about 1,500 feet per second.

Another important characteristic of the combustion chamber 2 is itsoverall cubic capacity in relation to the.

cross-sectional area of the nozzle 4..The cubic capacity of the chamber2 should be sufficiently large to provide for a period of outflow of gasthrough the nozzle which lasts sufficiently long to enable the period ofinjection of the charge of particulate material (which will be describedhereinafter) into the combustion chamber to be completed while thepressure in the combustion chamber still remains at a high level. Thus,in the preferred embodiment, wherein the injection period of the powdercan be accomplished in about5 milli-seconds, the period of gasoutflow"(sometimes called the blow down) during which gas escapes from,the' nozzle, should be several times longer. For example, a $4; inchinternal diameter nozzle requires a chamber volume of at least 8 cubicinchesgiving a blow down period of about 10 milli-seconds and inpractice a chamber capacity of 12-14 cubic inches isprovided. With thesedimensions, powder can be injected and substantially eliminated from thecombustion chamber 2 before the pressure in it has dropped to avaluegwhich is too low to'project the coating material against the workpiece with a sufficient velocity for satisfactory coating.

Various considerations affect the nozzle length. Nozzle length isdetermined by required powder impact velocity, powder particulate size,.and firing pressure, for a given velocity being proportional toparticle size and inversely proportional to firing pressure. Therequiredvelocity is that which" will hammer particles into a dense, well-bondedcoating; too much velocity. will break up in-place coating or evenremove substrate material while insufficient velocity leaves the coatingporous. Temperature plays a subordinate role by softening particles tofacilitate impact deformation but temperature is primarily gained fromexposure of the powder to hot gas by injecting across the combustionspace, with relatively little additionalheating occurring in the nozzle.Relatively high'firing pressure (related to available fuel and airsupply pressure) permits high velocity from a short nozzle; the nozzlecould be made much shorter than described here by proportionatelyincreasing firing pressure, or vice-versa, by manipulating powder sizeand/or fuel air supply pressure. For example applying a coating oftungsten carbide in the 325 mesh +15 micron size range, a satisfactorycoating was obtained, using a nozzle of 4 inches length, having anamorphous structure with a Knoop hardness of approximately 1,200, withadhesion in excess of 1 1,000 pounds per square inch using standardtests.

Important advantages obtained by using a relatively short nozzle arethat the relative significance of wall friction and wall heat losses aresubstantially reduced. By contrast, a soda straw nozzle, e.g., onehaving a length to diameter ratio in excess of 30, has a large amount ofwall surface area in relation to its crosssectional area with the resultthat wall friction appreciably slows down gas flow during passagethrough the nozzle and there is an additional relatively high heat loss.Additionally, the ability to function with a short nozzle facilitatesinstallation of the apparatus in locations where space is at a premium.By conducting combustion through a process of deflagration in thepresent invention rather than by detonation causing a supersonic shockwave, it is possible to avoid the need for a nozzle length sufficientlylong to sustain a detonation wave.

The process occurring in the combustion chamber with reference to thepressures and dimensions of the preferred embodiment described aredepicted graphically in FIG. 5. Starting a pulse or a flow at zero time,

combustible mixture at psi commences admission to the chamber throughthe inlet unit 8 (as will be described in more detail hereinafter) forabout 8 milliseconds. At about 5 milli-seconds, a charge of theparticulate coating material is injected into the chamber and injectionof the coating continues until it terminates at about 10 milli-seconds.About midway through the powder injection, after 7.5 milli-seconds haveelapsed, the spark plug 10 ignites the mixture causing a rapid rise inpressure within the combustion chamber to a peak value of about 400 psiattained at about 10 milli-seconds after commencement of the cycle.

This injection of the powder ceases at approximately the time thepressure in the chamber is at its peak value. At about that time thefirst particles injected have travelled out of the combustion chamber 2and through the nozzle 4 to impact the work piece, thus starting acoating period which continues for about 2 milli-seconds. The coatingperiod is shorter than the injection period because-.the later particlesinjected catch up with the earlier particles in the nozzle due to thepressure build-up in the chamber. By the end of the coating periodsubstantially all the particulate material has been blown out of thecombustion chamber 2 with the result that by the time the pressure inthe combustion chamber eventually falls below that necessary to sustainan adequate velocity for coating, all the particulate charge hasalreadybeen applied.

It will be appreciated that the pressures, times and dimensionsdescribed for the preferred embodiment can be selectively varied, if sodesired, to facilitate the use of larger or smaller coating apparatusesfollowing this invention. In addition the timing of the coating materialinjection period can be selected to commence after, rather than before,ignition for applications in which it is desirable to introduce thepowder into an atmosphere in which all-the oxygen has already beencombusted, to reduce particle oxidation.

The previously mentioned fuel inlet unit 8 (FIGS. 6 and 7) includes acylindrical inlet housing 30 having a reduced, threaded boss 32 at itsforward end which th'readedly engages the previously described bushing22 in the side of the combustion chamber 2. Extending rearwardly intothe inlet housing 30 from its forward end is an inlet passage 34 whichterminates at about the midpoint of the inlet housing. Extendingrearwardly from the inlet passage 34 through the remainder of the inlethousing is a second passage 36, of relatively smaller diameter, whichslidably receives a valve stem 38 carrying a valve head 40. The valvehead 40, which is beveled along its rim, seats on a correspondinglybeveled valve seat 42 on the inlet housing body 30 and closes off fluidcommunication between the inlet passage 34 and the combustion chamber 2in a closed position of the valve head.

To hold the valve head in its closed, seated position, the rearward endof the valve stem 38, which projects rearwardly beyond the inlet housing30, is provided with an undercut, annular groove 42 providing aforwardly facing shoulder 43 which is engaged by a circular collar orspring retainer 44. A circular compression spring 46 spacedconcentrically around the valve stem 38 extending between the inlethousing 30 and the collar 44 is just sufficiently strong to hold thevalve head 40 closed against the pressure exerted by the incoming supplyof combustible gas which is delivered continuously to the interior ofthe inlet passage 34 through a conduit 48 (FIG. 7).

To move the valve head 40 forwardly off its seat, thus placing the inletpassage 34 in fluid communication with the interior of the combustionchamber, two electrical solenoids 50 are fixedly mounted on the exteriorof the inlet housing 30 on opposite sides thereof. The solenoids 50 areof conventional construction, each having an electromagnetic coil 51(FIG. 9A) with a plunger 52 mounted for axial reciprocation forwardlyinto the coil when the coil is energized. Connected to and carried bythe plungers 52 is a transverse yoke 54 (FIG. 6) in continuous abuttingcontact with the free rearward end of the valve stem 38.

In a de-energized condition of the solenoids 50, the biasing spring 46urges the valve stem 38 to move the yoke 54 rearwardly so that theplungers 52 are in an extended rearward position when the valve head 40is seated. Energizing the solenoids 50, which causes the plungers 52 tomove into the solenoids, carries the yoke 54 forwardly (to the dottedline position shown in FIG. 6) carrying the valve stem 38 forwardly andraising the valve head 40 off its seat. At this time the combustiblemixture, which is at a pressure of 100 psi in the preferred embodiment,starts to feed into the combustion chamber 2. The solenoids 50 arede-energized at approximately the time the spark plug is fired. Therapid pressure build-up that then occurs in the combustion chamber 2during charging allows the spring 46 to return the valve head 40 to itsseat rapidly closing off the combustion chamber 2 from the inlet passage34 before the advancing flame front can reach the mixture in the inletpassage.

To prevent leakage of the combustion mixture outwardly of the inlethousing along the stem 38, which could create a fire hazard, an annularrecess 56 in the inlet housing 30 surrounds the valve stem atapproximately the midpoint of the second passage 36 (FIG. 7). Air isdelivered to the passage 56 through a conduit 58, at a higher pressurethan the pressure at which the combustible mixture is supplied to theinlet passage 34. As a result, any leakage of gas between the stem 38and the second passage 36 is in a direction from the recess 56 towardsthe inlet passage 34, preventing escape of combustible mixturerearwardly into the atmosphere. Additionally, in an alternativeembodiment of the invention in which the particulate material isintroduced into the chamber 2 through the fuel inlet valve by entrainingit in the fuel gas supply, the flow of gas introduced through the recess56 is very important for preventing powder from filling the passagearound the valve stem and jamming its swift movement between the openand closed positions.

To energize and de-energize the solenoids 50 for pulsed or cyclicalfeeding of mixture into the combustion chamber the electrical circuitshown in FIG. 9A is employed. The preferred rate of operation is at apulse rate in the region of 5-25 pulses per second although this may bevaried. The coil 51 of the solenoid 50 is connected in series with acapacitor 62 which is charged by a high voltage (300 volts) power supplyindicated by battery 64 when switch contacts 66a and 66b are closed.When switch contacts 66a and 66c are closed the capacitor 62 dischargesthrough the coil 51 of the solenoid moving the associated plunger 52forwardly. When the switch contacts 66a and 66b are remade the capacitor62 is recharged through coil 66 from power supply 64. A rectifying diode70 is included in the circuit to the solenoid coil 51 to prevent reversecurrent flow when the capacitor charge swings in its opposite polarity(FIG. 9B), insuring that the solenoid experiences only a single currentpulse. This circuit minimizes the electrical energy drain on the system.

Similarly to energize the spark plug 10 (FIG. 4) a capacitor 70 and aprimary coil 72 of a standard ignition transformer, having its secondarycoil 73 connected to the spark plug 10, are connected in series with abattery 74. A pair of switch contacts 76 are connected across inparallel with the capacitor 70. The switch contacts 76 are opened andclosed by movement of the valve stem 38. When the valve stem moves toopen the valve head 40 the points 76 close, starting current build-up inthe primary coil 72. As the valve stem closes the valve head 40, thepoints 76 reopen, initiating a voltage change across the coils of thetransformer which causes the ignition spark. Although a system utilizingonly one spark plug has been disclosed, it will be appreciated that theignition system may be readily modified to energize two of the sparkplugs 10 located on opposite sides of the combustion chamber 2.

As previously mentioned, a supply of combustible mixture is suppliedthrough the conduit 48 to the inlet passage 34 in the inlet unit 8. Thesupply of combustible mixture is from a source system shown in FIG. 2which includes a fuel air mixing tank 80 connected to the conduit 48, inwhich air and propane gas are mixed at a pressure of approximately psito provide the combustible mixture. When the inlet valve head 40 opens,the mixture flows through the conduit 48 and the inlet passage 34 intothe combustion chamber 2 which, after completion of the preceding pulse,is at a pressure substantially lower than 100 psi.

Air is supplied to the mixing tank 80 from an air surge tank 82connected to a high pressure source of air, such as an air line,operating at 100 psi. The air surge tank 82 is connected through anintervening conduit 84 to the mixing tank 80.

Propane gas is supplied to the mixing tank 80 from a bottle 86containing liquified propane, through connecting conduits 88. Positionedoutside the propane bottle 86 are electrical heating lamps 90 whichraise the temperature of the liquid propane so that it boils off. Theheating of the liquid propane creates a supply of propane gas at aboutpsi and it passes through a variable restrictor 92, interposed in theconduit 88, which controls the supply of propane into the mixting tank80. Connected in' the conduit 88 with a branch connection to the airconduit 84, is a slave regulator 94 which automatically regulates thesupply pressure of the propane gas to that of the air pressure.

Two safety features are included. A pressure sensor 98 in fluidcommunication with the propane gas in the conduit 88 is connected withthe electrical supply to the heating lamps 90 for the propane bottle, sothat if an excessive pressure rise is detected by the unit 98 itautomatically turns off the heating lamps. It is also necessary to turnoff the heating lamps 90 when the liquid propane in the bottle 86 hasbeen exhausted and for this purpose a weight-sensor indicatedschematically as 100, is also connected with the propane bottle. Theweight-sensor 100 cuts off the electrical supply to the lamps 90whenever the weight of the bottle 86 and its contents drops below apredetermined level.

The mixing tank 80 and the air surge reservoir 82 are of very muchlarger volumetric capacity than the combustion chamber 2 to minimizevariations in supply pressure of the combustible mixture during flow ofthe gas into the combustion chamber.

Although a source utilizing liquified propane gas has been disclosed, itwill be understood that, by appropriate modification, a liquid fuel ormist can be mixed with air and supplied to the combustion chamber toprovide the combustion mixture.

The previously mentioned powder injector unit 12 (FIG. 8) includes avertical, closed hollow cylindrical injector housing 120. The housing120 has a threaded boss 122 at its lower end which engages a threadedbushing 124 welded to and extending through the wall of the combustionchamber 2 at its upper end. A vertical passage 126, extending throughthe boss 122, places the interior of the injector housing 120 in fluidcommunication with the interior of the combustion chamber 2. The passage126 is normally closed, however, by an injector valve head 128 whichseats on an annular neoprene sealing ring 130 mounted in the lower endof the injector housing. The injector valve head 128 may be liftedvertically off its seat 130 by an injector valve stem 132 extendingupwardly and outwardly through the upper end of the injector housing120. The upper end ofthe injector housing includes a conventionalpressure type seal (not shown) permitting vertical sliding motion of thestem 132 without loss of pressure within the housing.

' Fixedly secured to the stem 132, adjacent the midpoint of the housing,is a piston 134 which divides the interior of the housing into an upperchamber 136 and a lower chamber 138. The piston 134 guides the valvestem for vertical sliding motion to insure that the valve head movesvertically off and onto its seat 130.

Particulate material is periodically fed into the lower chamber 138through a horizontal conduit 140 connected to and extending through thesidewall of the housing 120. At its opposite end the conduit 140communicates with the lower end of a dispenser unit 142 comprisinganupper, storage container 144 containing a supply of the coatingmaterial anda lower, hopper 146. The storage container 144 is a closed,vertical hollow cylinder having a'cone-shaped bottom wall leading into anarrow throat 148. Passing centrally through the storage unit 144 is avertical shaft 150 having a threaded region 152 at its lower endpositioned in the throat 148, spaced from the walls thereof. A valvehead 154 is threadedly secured to the bottom of the shaft 152 and has anupwardly directed conical portion which seats on a correspondinglyshaped seat at the lower end of the throat 148.

Normally, flow through the throat into the underlying hopper 146, whichis connected to the storage unit 144 by an intervening neck 160, isprevented by the valve head 154. However, the shaft 150 may beselectively moved downwardly so that particles can pass through thethroat l48into the hopper 146. In addition, the threads 152 at the lowerend of the shaft 150 help to carry particulate material downwardly intothe lower hopper. From the hopper 146 the particles pass through theintervening conduit 140 into the lower chamber 138.

By the use of both a storage unit and a hopper, the quantity of materialfed into the powder injector housing on each charge can be controlled.Moreover, by providing the hopper 146, it is insured that a volume ofparticulate material mixed with a relatively larger volume of air is fedthrough the conduit 140, thus avoiding clogging of the conduit as mightoccur if it were attempted to feed directly from the mass of material inthe storage unit into the conduit without an intervening hopper. v

As the particulate material must be fed into the combustion chamberduring a period in which the pressure in the chamber rises to a peak ofabout 400 psi, it is necessary to insure that the pressure in theinterior of each of the injector housing 120, the storage unit 144 andthe hopper 146 are all at a still higher pressure. For this purpose, asupply of air from a conventional higher pressure source at about 1,000psi (not shown) is connected through a supply'conduit 162 feeding branchconduits 164, 166 and 168 which areconnected .to the upper chamber 136,the interior of the-storage unit 144, and the interior of the hopper146, respectively.

To inject the material in the lower chamber 138, the stem 132 is raisedvertically, lifting the valve head :128 off its seat. The high pressurewithin the lower chamber 138 injects the particles into the combustionchamber in a direction toward the nozzle 4-. By injecting the particlesat the side of the combustionchamber remote from the nozzle 4, theparticles are given a sufficient residence time in thecombustion'chamber 2 to provide a necessary degree of preheatingbeforethey enter the high velocity combusted gas stream through thenozzle Return of the valve to its closed position thereafter is assistedby the high pressure on the upper side of the valve head 128 which givesa particularly rapid and effective valve closing action.

The valve stem 132 may be raised and lowered by the use of a solenoidand associated switching circuit, similar to one of the solenoids 50 andassociated circuits, previously described in connection with the fuelinlet unit. Thus, it will be appreciated that the fuel inlet solenoids,the powder injector solenoid and the spark plug are each energized inresponse to operation of the switches in their respective associatedelectrical circuits. As previously discussed, the .make and break pointsfor the spark plug, 10 are mounted on the inlet valve mechanisms so thattiming of the spark at the desired interval after opening of the inletvalve is achieved automatically. Similarly, the opening of the powderinjector valve in the timed relation previously described is achieved byarranging the switch contacts to the powder injector solenoid to closeapproximately 3 milli-seconds after the fuel inlet valve head 40commences to open. This can be achieved by mounting cams on a commonrotating shaft controlling the operation of the switches controlling theinlet valve and the powder injector plunger in the desiredtiming'relation. Other conventional timing circuits could alternativelybe used.

In an alternative embodiment of the invention, the coating materialinstead of being introduced into the chamber separately from thecombustible mixture, may be introduced into the chamber already mixedwith the combustible mixture. This may advantageously be done byintroducing the coating material into the line 48 between the fuel/airsource and the fuel inlet valve or, alternatively, by introducing thecoating material into the chamber 34 within'the fuel inlet valve 8 via asuitable conduit. In either event'the coating material enters thecombustion chamber with the combustible mixture.

What is claimed is:

1. An apparatus for applying particulate coating material to a workpiece comprising:

a combustion chamber having a gas inlet and a restrictive gas outlet,valve means in the gas inlet for blockingflow of gas fromthe chamber outthrough the gas inlet during combustion in the combustion chamber,

the combustion chamber having a cross sectional area substantiallylarger than that of the gas outlet such that a major portion of thegases will be retained in the combustion chamber by the restrictive gasoutlet while the combustible gaseousmixture is deflagrated whereby thepressure within the combustion chamber will rise sharply as a result ofsuch .deflagration, fuel feed means for forming a combustible gaseousmixture in the chamber by forcing gases through the gas inlet into thecombustion chamber, ignition means for igniting a combustible gaseousmixture in the combustion chamber, particle feed means for injecting apredetermined quantity of particulate coating material into gases ofcombustion in the combustion chamber, and

control means for thevalve means, fuel feed means,

ignition means and particle feed, means for respectively formingacombustible gaseous mixture in the combustion chamber, igniting thecombustible gaseous mixture to produce a sharp increase in pressure inthe combustion chamber, and injecting a predetermined quantity ofparticulate material into the chamber while a substantial .portion ofthe gases of combustion are still in the combustion chamber, whereby theparticulate material will be heated by the gases of combustion andaccelerated by the gases of combustion issuing from the gas outlet forimpact against a work piece.

2. The apparatus of claim 1 wherein the fuel feed means comprises:

fuel-air carburetor means for producing a combustible mixture of fueland air,

a source of air at a super atmospheric pressure, and

means connecting the source of air at super atmospheric pressure to thecarburetor and the output of the carburetor to the gas inlet of thecombustion chamber, and wherein the valve means controls the admissionof a fuel-air mixture from the carburetion means to the combustionchamber.

3. The apparatus of claim 2 wherein the fuel feed meanshas sufficientpressure capacity to force gas into the combustion chamber at a rategreater than the rate at which the gas escapes through the gas outlet toachieve a pressure substantially greater than atmospheric in thecombustion chamber prior to combustion of the gases. 1

4. The apparatus of claim 2 wherein the fuel-air carburetion meanscomprises:

a source of liquified natural gas,

a mixing tank in fluid communication with said internal passage in saidinlet valve housing, an air surge tank in fluid communication with asource of air under pressure and with said mixing tank for deliveringair under pressure thereto,

conduit means connecting said source of liquified propane gas and saidmixing tank; and

flow control means connected with said conduit means and with said airsurge tank for regulating the proportions of air and propane gas fed tosaid mixing tank.

5. The apparatus of claim 1 wherein the particle feed means comprises:

an injector housing having a closed injector chamber therein,

an outlet port in said injector housing placing one end of said injectorchamber in fluid communication with the interior of said injectorchamber in fluid communication with the interior of said combustionchamber,

an injector valve having,

an injector valve head which in a closed position thereof closes saidoutlet port,

I actuating means connected with said injector valve head extendingoutwardly of said injector housing for selective movement of saidinjector valve head to an open position exposing said outlet ports;

dispenser means connected with said injector housing for delivering acharge of the particulate material to said injector chamber in theregion of said valve head; and pressure means in fluid communicationwith said injector chamber for supplying gas thereto at a pressure inexcess of the peak pressure developed in said combustion chamber,whereby when said valve head is raised off said outlet port the pressurewithin said injector chamber is sufficient to inject the particulatematerial within said injector cham' her into said combustion chamber.

' 6. The apparatus'of claim 1 wherein the gas outlet is formed by anelongated nozzle of substantially constant diameter for accelerating theparticulate material.

' 7. The apparatus of claim 6 wherein said combustion chamber and saidnozzle are of generally circular cross section with the ratio of theinternal diameter of said combustion chamber to--theinternal diameter ofsaid nozzle being at least 5 to l.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO.3,915,381

DATED October 28, 1975 NVENTOMQ I Rosser B. Melton, In; John M. Clark,Jr.; Ronald J. Mathis;

William D. Weatherford, 3r.; Charles D. Wood, Ill.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 12, line 42, "ports" should be --port--.

Signed and Scaled this Second D3) Of November 1976 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer (ummisrimrer uj'Parenrsand Trademarks

1. An apparatus for applying particulate coating material to a workpiece comprising: a combustion chamber having a gas inlet and arestrictive gas outlet, valve means in the gas inlet for blocking flowof gas from the chamber out through the gas inlet during combustion inthe combustion chamber, the combustion chamber having a cross sectionalarea substantially larger than that of the gas outlet such that a majorportion of the gases will be retained in the combustion chamber by therestrictive gas outlet while the combustible gaseous mixture isdeflagrated whereby the pressure within the combustion chamber will risesharply as a result of such deflagration, fuel feed means for forming acombustible gaseous mixture in the chamber by forcing gases through thegas inlet into the combustion chamber, ignition means for igniting acombustible gaseous mixture in the combustion chamber, particle feedmeans for injecting a predetermined quantity of particulate coatingmaterial into gases of combustion in the combustion chamber, and controlmeans for the valve means, fuel feed means, ignition means and particlefeed means for respectively forming a combustible gaseous mixture in thecombustion chamber, igniting the combustible gaseous mixture to producea sharp increase in pressure in the combustion chamber, and injecting apredetermined quantity of particulate material into the chamber while asubstantial portion of the gases of combustion are still in thecombustion chamber, whereby the particulate material will be heated bythe gases of combustion and accelerated by the gases of combustionissuing from the gas outlet for impact against a work piece.
 2. Theapparatus of claim 1 wherein the fuel feed means comprises: fuel-aircarburetor means for producing a combustible mixture of fuel and air, asource of air at a super atmospheric pressure, and means connecting thesource of air at super atmospheric pressure to the carburetor and theoutput of the carburetor to the gas Inlet of the combustion chamber, andwherein the valve means controls the admission of a fuel-air mixturefrom the carburetion means to the combustion chamber.
 3. The apparatusof claim 2 wherein the fuel feed means has sufficient pressure capacityto force gas into the combustion chamber at a rate greater than the rateat which the gas escapes through the gas outlet to achieve a pressuresubstantially greater than atmospheric in the combustion chamber priorto combustion of the gases.
 4. The apparatus of claim 2 wherein thefuel-air carburetion means comprises: a source of liquified natural gas,a mixing tank in fluid communication with said internal passage in saidinlet valve housing, an air surge tank in fluid communication with asource of air under pressure and with said mixing tank for deliveringair under pressure thereto, conduit means connecting said source ofliquified propane gas and said mixing tank; and flow control meansconnected with said conduit means and with said air surge tank forregulating the proportions of air and propane gas fed to said mixingtank.
 5. The apparatus of claim 1 wherein the particle feed meanscomprises: an injector housing having a closed injector chamber therein,an outlet port in said injector housing placing one end of said injectorchamber in fluid communication with the interior of said injectorchamber in fluid communication with the interior of said combustionchamber, an injector valve having, an injector valve head which in aclosed position thereof closes said outlet port, actuating meansconnected with said injector valve head extending outwardly of saidinjector housing for selective movement of said injector valve head toan open position exposing said outlet ports; dispenser means connectedwith said injector housing for delivering a charge of the particulatematerial to said injector chamber in the region of said valve head; andpressure means in fluid communication with said injector chamber forsupplying gas thereto at a pressure in excess of the peak pressuredeveloped in said combustion chamber, whereby when said valve head israised off said outlet port the pressure within said injector chamber issufficient to inject the particulate material within said injectorchamber into said combustion chamber.
 6. The apparatus of claim 1wherein the gas outlet is formed by an elongated nozzle of substantiallyconstant diameter for accelerating the particulate material.
 7. Theapparatus of claim 6 wherein said combustion chamber and said nozzle areof generally circular cross section with the ratio of the internaldiameter of said combustion chamber to the internal diameter of saidnozzle being at least 5 to 1.